Electromagnetic Regolith Excavator

ABSTRACT

Decades of research and development have been invested in various forms of railguns, coilguns and mass drivers. See http://settlement.arc.nasa.gov/75SummerStudy/Table_of Contents1.html 
     Research at the Space Studies Institute in the 1980s refined the mass driver concept. See http://ssi.org/introduction-to-research/research-report/# mass-driver-iii 
     The innovation of the Electromagnetic Regolith Excavator is to eliminate the use of a bucket or other container that is accelerated by the magnetic fields. Instead, magnetic particles in the regolith itself (nickel-iron grains and/or magnetite) are put into motion and they carry along with them a to-be-determined fraction (perhaps all) of the co-resident non-magnetic regolith particles. 
     The Electromagnetic Regolith Excavator applies only attractive forces: no anchoring is required. This enables robotic and crewed spacecraft to safely collect surface material from asteroid targets that may be tumbling. Because no hard connection is required, no strong hazardous forces can be imparted to the collection apparatus aboard the spacecraft.

SUMMARY OF THE INVENTION

The Electromagnetic Regolith Excavator (ERE) is a proposed method of excavation (including drilling) that uses traveling waves of magnetism to draw magnetic materials into and through a tube and then to direct their movement into a collection bag. It takes advantage of the magnetic nature of most chondrite asteroids (whether in nickel-iron grains or in ferromagnetic minerals such as magnetite) to rapidly move large volumes of material. Non-magnetic materials are carried along with the magnetic portion, thanks to collisions, friction, inertia, and the careful timing of magnetic pulses.

The ERE behaves much like a vacuum cleaner: the open end attracts loose material, which then enters a duct and is moved along it by directional forces until it is deposited into a receptacle. A vacuum cleaner uses air pressure to draw in and move material, while the ERE uses magnetic attraction to draw in and direct the material. A vacuum cleaner depends upon friction between air and dirt, while the ERE depends upon friction between magnetic particles and non-magnetic ones in the existing regolith.

Near Earth asteroids (NEAs) are key resources for the cost-effective exploration and settlement of space. However, the microgravity environment results in several challenges for asteroid exploitation, including the difficulty of processes—such as digging—that we take for granted on the Earth's surface. Most large asteroids are likely rubble piles, very loosely held due to their low self-gravity. Collisions and impacts of small bodies tend to fragment aggregates into smaller and smaller particles, often resulting in a fine-grained outer covering called regolith. To excavate a bucket of regolith, a down force must be applied to push the blade of a bucket into the regolith—and that down force generates a Normal Reaction force which thrusts the excavator upward, away from the asteroid. The same thing happens when drilling is attempted. In order to begin drilling, the drill head is pressed into the regolith, an action that immediately results in the drilling machine pushing away from the asteroid. Obvious solutions—attaching the spacecraft in some way to the asteroid—are cumbersome if the spacecraft must be able to traverse the asteroid's surface gathering material.

The Electromagnetic Regolith Excavator (ERE) is a proposed method of excavation (including drilling) that circumvents these problems. The ERE uses traveling waves of magnetism to draw magnetic materials interspersed in the asteroid regolith and then to direct their movement. It takes advantage of the magnetic nature of most chondrite asteroids (whether in nickel-iron grains or in ferromagnetic minerals such as magnetite) to rapidly move large volumes of material. Non-magnetic materials are entrained or carried along with the magnetic portion, thanks to collisions, friction, inertia, and the careful timing of magnetic pulses.

The electromagnetic mouth and throat of the ERE accelerate ferrous grains in the surface material toward a collector in the spacecraft. Ferromagnetic soil particles are expected to be mingled with nonferrous particles in many asteroids' overall regolith matrix, similar to the mix found in ordinary chondrite meteorites. Because there is negligible gravity, the collision forces of ferrous grains hitting other constituents is sufficient to entrain a significant fraction of the nonferrous grains.

The ERE may be viewed as a very-low-velocity coilgun. However, the extremely low velocities required (less than 1.0 meter per second on an asteroid) should ameliorate the known issues with coilgun designs.

The ERE may also function as a regolith drill, or ‘mole’, since by leaving it in one place it would excavate the material at that spot and could then be continuously lowered to remove still deeper material.

The forces and pathways can be tuned to keep all particles together, or to sort them into distinct streams of ferrous and nonferrous material.

Note that a regolith-recovery spacecraft may be equipped with several EREs, and at any one time, all but one unit may be acting as anchors or feet and one as an excavator/drill. After a time the duty cycle may shift to a different unit.

BACKGROUND OF THE INVENTION

The excavation of asteroidal regolith is totally untried technology, and there is no ‘current art’. It is, however, widely recognized that any mechanical excavation operation will develop a Normal Reaction Force which will tend to drive the excavation machine away from the surface being excavated, and that anchoring against this Normal Reaction Force is widely recognized to be presently unsolved.

The ERE uses and relies on the unusual fact that a significant fraction of the mass making up the regolith of both S class and C class asteroids is likely to be magnetic or magnetizable (ferromagnetic). It also uses the concept that this magnetic property will allow regolith particles to become mobilized by an appropriately pulsed magnetic traveling wave, and that furthermore this may entrain commingled non-magnetic regolith particles. The attraction of the magnetic fields to the regolith and the net reaction to the movement of that regolith results in a downward Normal Reaction Force which allows the invention to remain in place during operation, without requiring additional anchoring or thrusting.

A downstream add-on may use a principle similar to that of cross-belt magnetic separators, as used in the mineral sands industry, to separate magnetic and non-magnetic materials.

While the principle application of this invention is the excavation and movement of asteroid regolith, by suitable modifications of the invention it may also be used as a drill or as an anchor.

The ERE is, in fact, an electromagnetic anchor, excavator, drill, and separator, depending on ‘tunable’ details of its design and operation.

The Electromagnetic Regolith Excavator enables robotic and crewed spacecraft to safely collect surface material from asteroid targets that may be tumbling; because no hard connection is ever established (unless the ERE is intentionally used as a drill or anchor), no strong hazardous forces can be imparted to the collection apparatus aboard the spacecraft.

An Electromagnetic Regolith Excavator makes sample acquisition from asteroids and Phobos/Diemos more practical and less hazardous than with harpoon-style hard connection approaches. The absence of a hard connection also makes the extraction device easily mobile; alternative digging or drilling methods require the machine deploying the blade or drill to be anchored to provide resistive force to the digging or drilling motions. Releasing such anchors and then re-anchoring during a traverse will be cumbersome. By contrast, the ERE generates an attractive force toward the asteroid as it accelerates regolith the other direction into its collection chamber.

The stream of regolith gathered by the ERE can be split to deposit ferromagnetic particles into a collection chamber separate from the rest of the mass. This provides a rich feedstock for creating metallic parts, while the nonferromagnetic portion can be heated to release volatiles for propellants and life support, with the leftover rock used for radiation shielding.

State-of-the-Art for asteroid regolith excavation is theoretical, since no robotic or crewed missions have accomplished this feat. NASA's upcoming asteroid sampling mission, Osiris-REx, employs a momentary contact method: the spacecraft sampler rams the target at extremely low speed (0.1 m/s) and nitrogen squirts out to fluidize the regolith for capture. The repeated impacts pose a risk to the spacecraft.

By contrast, the Electromagnetic Regolith Excavator does not expose the host spacecraft to ramming shocks. The ERE also provides the safety of not establishing a hard connection with the asteroid, in contrast with methods that harpoon the target from a free-flying spacecraft. The ERE avoids the danger of entanglement if the harpoon cannot be withdrawn, or if the tumble of the target imparts large disturbances to the spacecraft during a nominal sampling activity.

Additionally, the reaction to the magnetic forces drawing material into the ERE serves to hold the ERE against the asteroid—no other anchoring method is required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram of a simple implementation of the invention: a single, simple tube with a series of independently controlled electromagnets along its length. The callouts are:

-   -   1. A hollow tube which holds the electromagnets and guides the         material being moved.     -   2. A series of electromagnet coils which attract the regolith         when energized.     -   3. The wires used to energize the individual electromagnet coils     -   4. The wires supplying current to the coil controllers     -   5. The wires passing control signals enabling/disabling the coil         controllers     -   6. The coil controllers which supply current to the attached         coil when selected by the computer.     -   7. The power supply for the electromagnetic coils.     -   8. The computer which controls the sequencing and operation of         the controllers, and thus the electromagnetic coils.

FIG. 2 shows a tube with multiple segments and a receiving container.

-   -   15. A fixed-angle segment connector     -   16. A flexible segment connector     -   17. Arrows depicting the directions of motion provided by the         flexible connector 16.     -   18. A container (a tank, canister, bag, or other device) to         receive and hold the excavated regolith.

FIG. 3 shows a variant of the ERE with a flat entry plate 9 to prevent regolith from climbing the exterior of the tube 1.

FIG. 4 is a bottom view of the ERE of FIG. 3, showing a grating 6 to prevent entry of particles large enough to clog the tube interior 5.

FIG. 5 shows a variant of the ERE with a constricted entrance 12 to prevent entry of particles large enough to clog the tube 1 interior.

FIG. 6 shows the bottom view of the ERE of FIG. 5, revealing that no grating is required since the entrance 11 of the constricted tube 12 is significantly smaller than the diameter of the interior of the tube.

FIG. 7 shows a variant of the ERE with a flared tube entrance 14 and a larger gathering coil 13.

FIG. 8 is a bottom view of the ERE of FIG. 7, showing that the flared entrance 14 must have a grating 10 to prevent large particles from entering and clogging tube 11.

FIG. 9 shows a computerized multi-color rendering offering a potential specific example of usage.

FIG. 10 shows a computerized multi-color rendering offering a potential specific example of usage.

DETAILED DESCRIPTION OF THE INVENTION

The Electromagnetic Regolith Excavator consists of a transport tube 1 constructed of non-magnetic material, and various configurations of electromagnetic coils 2 at or near the entrance and along the tube. The tube may or may not be flexible, may or may not be straight, and it ultimately dumps the moving material into a collection bag or other container 18 beyond the reach of the last magnet. The spacing of the coils, the strength of their magnetic fields, and the timing and shape of the magnetic waves that attract the regolith and move it along the tube are parameters to be determined by experimentation in a microgravity environment.

The controller is a software-controlled, possibly camera guided electric sequencer. The sequencer computer 8 individually activates the coil controllers 6 via control wires 5 which, when activated, apply current to the selected coil via wires 3. The coil controllers 6 are powered via a current source power supply 7 using wires 4.

In normal (excavating) operation, the coil nearest the asteroid will be energized to attract the magnetic content of the adjacent regolith, and just before the first particles reach it, power is switched to the next coil in the path, and so on until the material is allowed to deposit into the regolith collector (not shown). The momentum of the particles is expected to carry the bulk of the non-magnetic material as well. Note that exposed surface magnetic particles may be drawn quickly during initial operation, but subsequent waves will attract deeper particles, and these will necessarily impart momentum to the non-magnetic material that surrounds them.

Specific Examples of How to Practice the Invention

To excavate regolith on an asteroid (or other similar body such as the Mars moons Phobos and Deimos), a spacecraft will maneuver one end of the invention adjacent to the regolith surface. The sequencer will energize the coils 2 in sequence to move the magnetic portions of the regolith, and via friction the non-magnetic portions as well, into and through tube 1 until the regolith is deposited into a container 18 at the opposite end.

Note that the ERE tube may consist of multiple segments (see FIG. 2), which may be curved (not shown) or angled via a fixed connector 15, and which may be articulated via a flexible connector 16 and a mechanism (not shown) to control the movement such that the tube can be moved both vertically (not shown) and about and around (directions of movement 17) the surface of the asteroid to gather regolith from an extended area. In operation, the ERE will behave much like a vacuum cleaner to draw and move large quantities of material (by using magnetic fields instead of air pressure).

By moving the opening of the ERE vertically instead of horizontally, it will function as a drill through the loose regolith.

Once the ERE (in drill mode) has penetrated the surface sufficiently, the coils may be simultaneously energized, which will enable the ERE tube to function as an anchor.

The opening (entrance) to the ERE tube may be implemented as a straight tube as in FIG. 1 and FIG. 2, or

-   -   1. To prevent the entrance of potentially clogging particles, it         may have         -   a. A smaller-diameter opening (FIG. 5 and FIG. 6) such that             only particles small enough to freely move through the             larger tube can be admitted, or         -   b. Covered with a grating 10 that prevents the entrance of             too-large particles as shown in FIG. 4 and FIG. 8.     -   2. To prevent the movement (and subsequent loss of efficiency)         of magnetic material up the outside of the tube, it may be         implemented as a:         -   a. Large-diameter cone 14 (as shown in FIG. 7 and FIG. 8)             that extends beyond the normal reach of the first magnetic             coil, or         -   b. A flat plate 9 (as shown in FIG. 3 and FIG. 4) which             extends beyond the effective attraction width of the first             coil         -   c. These larger cones or plates may have additional, larger             magnetic coil(s) 13 (as shown in FIG. 7) as the first             coil(s) to attract and thus motivate larger volumes of             material at one time.     -   3. The magnetic movement of material up the outside of the tube         may, however, be advantageous when the invention is used as a         drill.     -   4. Reversing the sequence of coil activation and thus directing         the particles down the outside of the tube is useful when         extracting an ERE tube used as an anchor.

While the above process describes a single clump of material entering, moving through, and leaving the apparatus, by using suitable minimum spacing between successive energized coils, several clumps may be moved simultaneously, in synchronization or not. Once moving, the regolith may move at a constant average velocity, or may be accelerated to different velocities as needed.

Clump control (via shaping of magnetic fields) may be used to confine, as much as practical, the extent of the individual clumps and/or their relative position within the tube, which may allow for improved efficiency in mass moved per clump or per unit of time.

Optical, mechanical, electromagnetic, or radio-frequency (metal detector) methods may be used to sense the movement of a clump, potentially improving the efficiency of material movement, either by allowing higher velocities or more closely spaced successive clumps. 

1. A system of gathering and directing asteroid or planetary regolith containing sufficient ferromagnetic content via traveling waves of magnetism applied via a series of electromagnetic coils.
 2. A method of (1) where the material is gathered into a tube (or series of tubes), at least one of which has magnetic coils, so that the entrained material may be directed as desired.
 3. A method of (2) where the tube(s) are articulated such that they may be moved vertically and horizontally about the surface to increase the volume of regolith that may be gathered.
 4. A method of (2) where the tube(s) are flexible and the opening may be moved independently about the surface.
 5. A method of (1) where the magnetic content of the regolith is primarily nickel-iron grains and/or magnetite.
 6. A method of (1) where the regolith moves along the outside of the magnetic coils, rod, or tube, constrained only by momentum and/or magnetism.
 7. A regolith drill, wherein a tube (as in 2) or a rod (as in 6) is moved vertically to excavate the material from a single column of regolith.
 8. A regolith anchor, wherein a regolith drill (as in 7) is operated to set the tube or rod at depth, and then the magnetic fields are simultaneously activated to provide fraction and effectively hold an increased mass of material against the anchor.
 9. A method of (8) where electromagnetic coils are used to drill into the regolith and then permanent magnets (or permanently magnetizable coils) are used to maintain the anchor after power is removed. 